A capacitive pressure transducer converts changes in pressure applied to its diaphragm, such as by a fluid, into corresponding capacitance changes to enable pressure measurements. Behind the diaphragm is a pressure cavity with parallel offset conductive plates that compose a variable capacitor to detect strain due to applied pressure on the diaphragm, where one of the parallel offset conductive plates is in a fixed position relative to the diaphragm and the other is affixed to the diaphragm.
Typical pressure sensors include two major parts: (i) an element affected by pressure changes, such as a capacitive pressure transducer, and (ii) electronics for providing a modulated electrical signal to the capacitive pressure transducer and for detecting effects on the modulated signal imparted by the capacitive pressure transducer as a function of the pressure changes.
Typical capacitive pressure transducers use metal, ceramic, or silicon diaphragms to which one parallel offset conductive plate is attached. The other plate is attached to a substrate that is insensitive to pressure changes. Pressure changes induce flexion in the diaphragm, which change the distance between the parallel offset conductive plates, causing a measurable change in capacitance. This change may or may not be linear and is typically no more than a few picofarads out of a total capacitance of 5-100 pF. This change in capacitance may be used to control the frequency of an oscillator or to vary the coupling of an AC signal. The electronics for signal conditioning are commonly located close to the transducing elements, preventing errors due to stray capacitance.